U.S. Pat. No. 4,674,303 to Paul J. Salcone discloses a safety lock for seat belt buckle providing a locking portion (28) on the housing portion which however should require a key for unlocking the lock. To hold such a key for an instant unlocking use may cause inconvenience for the user. If the key is missing, it will become a difficulty to release the seat belt buckle.
U.S. Pat. Nos. 4,685,315 and 4,691,539 respectively teach a strap lock and band lock, which however requires a key for unlocking the lock, possibly causing inconvenience to the lock user and causing embarrassment when losing the key especially when travelling or sporting outside the user's home.